The present invention relates to an improved polyarylene sulfide resin composition. More particularly, the present invention is concerned with a polyarylene sulfide resin composition and a molded article thereof having improved properties relative to preventing corrosion and staining of a metal combined with the molded article such as an electric contact.
In recent years, thermoplastic resins having a combination of high heat resistance and chemical resistance with flame retardancy have been desired for electrical and electronic equipment component materials, automobile equipment component materials, and chemical equipment component materials.
Polyarylene sulfide resins including polyphenylene sulfide are among the resins capable of meeting this desire. The demand for polyarylene sulfide resins has expanded also because polyarylenesulfides have excellent properties for the cost.
However, polyarylene sulfide resin has a drawback in that the raw material for production of the resin contains both sulfur and chlorine atoms and as a result by-products containing a large amount of chlorine are formed during synthesis of the resin. Unfortunately, this causes a problem when polyarylene sulfide resin is used as a material for molded components, since metals such as metallic contacts and plated or deposited metallic surfaces in the molded components are corroded and stained. As a result, polyarylene sulfide resin is poor in reliability because metal-polyarylene sulfide composite articles fail to sufficiently exhibit their intended function.
Because of the above-described problem, at the present time, polyarylene sulfide resin cannot be effectively for components which are continuously exposed to high temperature and which have a metallic contact, and thus, such problem limits range of applications of the resin.
The following expedients are known for solving the above problem.
(1) In the manufacturing process of the resin, the amount of inclusion of impurities such as sodium chloride in the resin is reduced by intensively purifying the resin.
(2) A trapping agent is positively added to suppress the formation of corrosive impurities. Examples of trapping agents include calcium carbonate, lithium carbonate (cf. Japanese Patent Laid-Open Nos. 162752/1979 and 229949/1985), hydrotalcite (cf. Japanese Patent Laid-Open No. 275353/1986), and zinc oxide (cf. Japanese Patent Laid-Open No. 181408/1984, Japanese Patent Publication No. 45711/1988 and U.S. Pat. Nos. 4,659,761 and 4,740,425).
(3) The resin is treated at a temperature as high as 200.degree. C. or above to reduce corrosive gases before use.
However, the above methods have respective problems and do not provide any satisfactory solution to the problem. Specifically, it has been found that method (1) wherein the resin is intensively washed can remarkably reduce the, content of sodium chloride but, such method scarcely results in any improvement in preventing corrosion of metallic components contained in the molded articles, e.g., silver, aluminum, or iron.
In method (2), it has been found that lithium carbonate reduces generation of chlorinated gas and exhibits the effect of preventing corrosion of some metals such as iron but, exerts no effect on silver and its alloys usually employed in the metallic contact. Further, neither calcium carbonate, hydrotalcite, zinc oxide, etc. prevent corrosion of silver.
It has also been found that method (3) causes side effects such as discoloration and deterioration of the resin matrix at high temperature and results in only a slight effect of preventing corrosion of metals such as silver, aluminum, iron, etc., so that this method has not been regarded as practical.
In order to improve the prevention of the corrosion and staining of a metal during and after molding without detriment to excellent heat resistance, solvent resistance, flame retardancy, and mechanical properties of a polyarylene sulfide resin composition, particularly a polyphenylene sulfide resin composition, the present inventors have attempted to determine which gases are generated when a polyarylene sulfide resin composition is heated and have searched for an additive for trapping these gases.